Month: March 2017

We discussed earlier about indexing, and specifically reverse key indexing.

I mentioned that is a solution for buffer busy waits on numerical consecutive inserted keys (like the sequence based generated ones) .

This post will test that solution.

For regular index test, I’ve created the following table, sequence and associated index:

create table test_tb
( row_id number
, text varchar2(100));

create sequence test_seq start with 1 increment by 1 cache 10000;

create index test_nidx on test_tb(row_id);

and a simple procedure that will insert the rows:

create or replace procedure insert_n (p_rows number default 10000) as 
begin
 
 for i in 1..p_rows loop
 insert into test_tb
 select test_seq.nextval, 'test row '||test_seq.currval from dual;
 
 end loop;
 commit;
end;
/

 

For the reverse key index test:

create table test_tb2
( row_id number
, text varchar2(100));

create sequence test_seq2 start with 1 increment by 1 cache 10000;

create index test_ridx on test_tb2(row_id);

and a simple procedure that will insert the rows:

create or replace procedure insert_r (p_rows number default 10000) as 
begin
 
 for i in 1..p_rows loop
 insert into test_tb2
 select test_seq2.nextval, 'test row '||test_seq2.currval from dual;
 
 end loop;
 commit;
end;
/

To test the effect of concurrent inserts, I’ve executed both procedures from 3 sessions (please note in my case number of sessions is small, but will still show us the impact of the two types of indexes):

execute insert_n(100000);

execute insert_n(100000);

Now looking at the buffer busy waits we had we see a reasonable benefit already of the reverse key index:

select object_name, value, statistic_name,object_type
from v$segment_statistics
where owner='C##INSIGHT'
and object_type='INDEX'
and statistic_name='buffer busy waits'
and object_name like 'TEST%'
;